1. Field of the Invention
This invention relates to a method for manufacturing toothpaste which can facilitate homogeneous mixing of an abrasive, a humectant, a binder, a surfactant, water, etc. and facilitate continuous manufacture.
2. Prior Art and Its Problem
The conventional industrial method for manufacturing toothpaste comprises the steps of swelling and dissolving a binder in a mixture of a humectant and purified water, under heating if required, to prepare a solution in which the binder is completely swollen and then kneading a powdery abrasive into the thus prepared solution before the kneaded mixture is homegeneously combined with a surfactant, a flavor, an effective ingredient, etc., followed by deaerating the thus prepared mixture. In addition to this method, there are various methods for manufacturing toothpastes which are disclosed in the Japanese Patent Publication No. 35-7699 and the Japanese Patent Application Laid-open Nos. 48-40947 and 52-108,031, etc.
There is another method for manufacturing toothpaste free from air bubbles which is specified in the Japanese Patent Application Laid-open No. 58-208,208 an comprises the steps of mixing and abrasive into water or a liquid mixture composed of water and a humectant before deaeration and then adding a binder dispersed in a humectant to swell and dissolve the binder in the mixture. However, although this method is an effective batch-type manufacturing method, it is difficult to continuously and homogeneously supply a binder dispersed in a humectant because the binder easily becomes deposited and the deposited binder cannot be readily dispersed again. The incomplete dispersion of the binder may result in wide variety of the viscosity of the final product (toothpaste). Further, since the binder is rapidly swollen and dissolved in the production process to increase the viscosity of the slurry, the specific apparatus fit for high viscosity is required. Therefore this method is not suitable for continuously manufacturing toothpaste.
The method for manufacturing toothpaste free from air bubbles specified in the Japanese Patent Application Laid-open No. 58-208,209 comprises the steps of dispersing a powdery mixture containing an abrasive and a binder in a liquid mixture containing a humectant and water to prepare a slurry before deaerating it while particles of the binder exist in the slurry and then aging the deaerated slurry until the particles of the binder are completely swollen and dissolved. Although this method enables continuous manufacturing of toothpaste, the slurry must be deaerated immediately after its preparation. Additionally, there are some cases where the particle diameter and the type of the binder used, dispersion temperature and similar conditions are restricted.